The present invention relates to a novel developer solution for an actinic ray-sensitive resist. More particularly, the invention relates to a practically useful developer solution for an actinic ray-sensitive resist capable of forming a finely patterned resist layer without film residue or deposition of scum and giving a high resolution of the pattern even in and around an extremely fine through-hole without decreasing the heat resistance of the patterned resist layer.
It is a well established technology, in the manufacture of semiconductor-based integrated circuits as well as masks for the manufacture thereof, printed circuit boards, planographic printing plates and the like, to use a so-called actinic ray-sensitive resist, which is a material having sensitivity to various kinds of actinic rays such as ultraviolet light, X-rays, electron beams and the like with an object to selectively or pattern-wise protect the surface of the substrate which undergoes a pattern-wise treatment of etching, diffusion and so on. Thus, the substrate surface is coated all over with a resist composition to form a coating layer of the resist which is then irradiated pattern-wise with actinic rays to form a latent image of the pattern followed by a development treatment with a developer solution, which pattern-wise dissolves away the resist layer, to form a patterned resist layer which serves for the protection of the substrate surface.
The actinic ray-sensitive resist materials can be classified into positive-working and negative-working ones depending on the types of the sensitivity characteristics to the actinic rays. Namely, a positive-working resist is imparted with increased solubility in the developer solution in the areas of the resist layer exposed to the actinic rays so that the resist layer in the unirradiated areas remains undissolved by the development treatment. The solubility behavior of a negative-working resist is reverse to that of the positive-working one.
Among the various types of the developer solutions used in the development treatment of a resist layer, most conventional are aqueous alkaline solutions prepared by dissolving an alkaline substance in water or a liquid mixture mainly composed of water. It is well known that, when the developer solution is to be used in the manufacturing process of semiconductor silicon-based devices, the alkalinity of the developer solution cannot be made by using an alkaline compound containing a metallic element such as sodium since contamination of semiconductor silicon with sodium causes adverse influences on the characteristic performance of the semiconductor devices. Therefore, it is conventional to prepare an aqueous alkaline developer solution by using an organic basic compound containing no metallic element such as quaternary ammonium hydroxide including tetramethyl ammonium hydroxide disclosed in IBM Technical Disclosure Bulletin, volume 3, No. 7, page 2009 (1970) and choline, i.e. trimethyl 2-hydroxyethyl ammonium hydroxide, disclosed in U.S. Pat. No. 4,239,661.
Along with the recent trend toward a higher and higher density of integration in semiconductor devices, the requirement for the fineness of patterning is increasing to such an extent that the line width of the patterned resist layer should be 1 .mu.m or even smaller. A proposal has been made, for example, in U.S. Pat. No. 4,820,621 according to which an aqueous alkaline developer solution mentioned above is admixed with a non-ionic surface active agent, such as alkylphenol polyethylates, in order to improve the wetting behavior of the resist surface with the aqueous solution in any finest pattern, especially, for patterning of very fine through-holes. When patterning of a resist layer is undertaken by using such a developer solution containing a nonionic surface active agent, occurrence of film residue or deposition of scum is sometimes unavoidable on the resist layer after development to cause a serious drawback in fine patterning for the manufacture of semiconductor devices. This problem can be partly solved by undertaking an overly exposure or overly development but no complete solution of the problem can be obtained thereby.
It is usually practiced that the film residue or scum is removed by subjecting the patterned resist layer on the substrate surface after development of the resist layer by lightly subjecting the resist layer to exposure to oxygen plasma or to a sputtering treatment. This measure, however, causes another problem that the shoulder portions in the cross sectional profile of a line pattern of the resist layer are rounded resulting in a decrease of the protecting performance of the resist layer or poor reproduction of the desired pattern. In particular, the treatment with oxygen plasma has a problem in the poor controllability of the plasma generation and, in addition, removal of scum can never be complete in and around very fine through-holes of a dimension of 1 .mu.m or finer in diameter due to the poor uniformity of the plasma treatment.
Alternatively, Japanese Patent Kokai No. 61-167948 proposes admixture of an aqueous alkaline developer solution with a non-ionic surface active agent of a different type such as polyoxyethylene nonylphenyl ether. Although the problem of deposition of scum or occurrence of film residue after development can be solved at least partly, another problem arises thereby that the heat resistance of the patterned resist layer may be adversely influenced so that fidelity of the pattern reproduction is decreased in the heat treatment of the patterned resist layer after development.